The invention relates to an aerostatic or aerodynamic bearing (hereinafter referred to as an air bearing) comprising a stationary part and a movable part with co-operating bearing surfaces which are separated by a bearing gap which at one area communicates with an air inlet and at another area opens into the atmosphere.
In the case of an aerostatic bearing, air can be supplied under pressure to the bearing gap through the inlet.
In the case of an aerodynamic bearing, the bearing surfaces bounding the gap are provided with at least one pattern of grooves which, in the operation of the bearing, build up a pressure in the air contained in the bearing gap and pump the air from the inlet to the atmosphere.
In air bearings of the above kind, the bearing clearance is only a few .mu.m.
Air from the surrounding atmosphere is often used as a lubricant for these bearings. Due to the small dimension of the bearing gap, dust particles present in the air contaminate the bearing gap to the detriment of the operation of the bearing. In order to avoid this it has been proposed to supply the air through filters to the bearing gap. However, this has proved inadequate because contamination still occurs at the outlet side of the bearing gap. This can be explained as follows. If due to load--and/or geometry--some cooperating bearing surfaces do not move in exactly parallel planes in the case of an axial bearing or exactly concentrically with each other in the case of a radial bearing, both positive and negative pressure differences occur in the bearing gap with respect to the surrounding atmosphere. These pressure differences continue as far as the periphery of the bearing gap, which may result in air flowing out of the gap over one part of the area at which the bearing gap opens into the atmosphere and air flowing in over another part. In this way dust particles present in the air enter the bearing gap, where they can get stuck. An adequate circulation of filtered air through the bearing gap for preventing a negative pressure occurring in regions of the gap cannot be obtained in an aerodynamic bearing while still maintaining a sufficient bearing capacity and stability. In aerostatic bearings also this causes problems in connection with the larger quantities of air that have to be pumped.